The present invention relates to the field of powering data terminal equipment and more particularly to providing power over data communication cabling constituted of a single pair.
Ethernet communication, also known as IEEE 802.3 data communication, is typically implemented over a structured cable having 4 twisted wire pairs. Power of Ethernet (PoE), as described in IEEE 802.3af—2003 and IEEE 802.3.at—2009, as published by the Institute of Electrical and Electronics Engineers, New York, the entire contents of each document is incorporated herein by reference, is superimposed over the data utilizing phantom powering. In particular, the existing data transformers of Ethernet are center-tapped, and thus the DC current through the two halves of the transformer are of equal magnitude and opposite direction leaving no net flux in the transformer core.
Ethernet communication for speeds less than 1000 megabits per second (Mbps) is typically supplied over 2 twisted wire pairs, one of the pairs being used as a transmit pair from the hub equipment to the data terminal equipment (DTE), which when powered by PoE is also known as a powered device (PD), and a second of the pairs being used as a transmit pair from the data terminal equipment to the hub equipment. The other two pairs were typically not used, and were known as spare pairs. The term transmit is typically abbreviated TX and the term receive is typically abbreviated RX for simplicity. In such an embodiment either spare powering, or data pair powering, may be implemented.
FIG. 1A illustrates a high level block diagram of an arrangement 10 for powering a PD from a switch/hub equipment 30 using phantom powering in accordance with the above standards. Arrangement 10 comprises: switch/hub equipment 30 comprising a first and second data pair 20, a power sourcing equipment (PSE) 40, and a first and second data transformer 50; four twisted pair data connections 60 constituted in a single structured cable 65; and a powered end station 70 comprising a first and second data transformer 55, a first and a second data pair 25, and a PD 80. Powered end station 70 is also known as the DTE.
The primary of each of first and second data transformers 50 are coupled to respective data pairs 20. An output and return of PSE 40 are connected, respectively, to the center tap of the secondary of first and second data transformers 50. The output leads of the secondary of first and second data transformers 50 are respectively connected to first ends of a first and a second twisted pair data connection 60 of structured cable 65. The second ends of first and second twisted pair data connections 60 are respectively connected to the secondary of first and second data transformers 55 located within powered end station 70. The center tap of the secondary of each of first and second transformers 55 is connected to a respective input of PD 80. Third and fourth twisted pair data connections 60 of structure cable 65 are connected to respective inputs of PD 80 for use in an alternative powering scheme known to those skilled in the art. In another embodiment, as will be described further below, third and fourth twisted pair data connections 60 further carry data. First and second data pairs 25 are coupled to the primary winding of each of first and second data transformers 55 and represent data transmitted between powered end station 70, particularly PD 80, and switch/hub equipment 30, each direction provided on a respected twisted pair data connection 60.
In operation, PSE 40 supplies power over first and second twisted pair data connection 60, thus supplying both power and data over first and second twisted pair data connections 60 to PD 80. As described above, since power is transmitted and received via the center tap of the respective transformers 50, 55 DC flux does not build up in the respective transformers 50, 55 responsive to power from PSE 40.
For speeds of 1000 Mbps, also known as Gigabit Ethernet, all 4 pairs are utilized for data communication, and each of the 4 pairs provide bi-directional communication. Thus, at both the hub equipment and at the DTE end, both a transmitter and a receiver are coupled to each pair. Arrangement 100 of FIG. 1B illustrates such an arrangement. Arrangement 100 is in all respects similar to arrangement 10, with the exception that data pairs 20 are provided coupled to each of the four twisted pair data connections 60 via respective transformers 50 and similarly four data pairs 25 are coupled to respective twisted pair data connections 60 via respective transformers 55. As indicated above each of data pairs 20, 25 are implemented as bidirectional transmitter receiver pairs as will be described further below, responsive to a respective hybrid circuit.
FIG. 2 illustrates a high level block diagram of an arrangement 100, known to the prior art, to provide bidirectional communication over each twisted pair data connection 60. At each end a transmitter 110, a receiver 120 and a hybrid circuit 130 is provided. The output of each transmitter 110, comprising a differential pair, is coupled to a respective differential input of the respective hybrid circuit 130 and the input of each receiver 120, comprising a differential pair, is connected to a respective differential output of the respective hybrid circuit 130. A bi-directional port of hybrid circuit 130 at the hub side, comprising a differential pair, is coupled to the primary winding of transformer 50 and presents data pair 20 and a bi-directional port of hybrid circuit 130 at the PD side, comprising a differential pair, is coupled to the primary winding of transformer 55 and presents data pair 25. The secondary winding of transformer 50 is coupled to a first end of a respective twisted pair data connection 60 and the secondary winding of transformer 55 is coupled to a second end of the respective twisted pair data connection 60.
Each hybrid circuit 130 is arranged to channel data transmitted by the coupled transmitter 110 towards twisted pair data connection 60 and away from the coupled receiver 120. Hybrid circuit 120 may be implemented electronically or magnetically, as known to those skilled in the art, although typically electronic hybrid circuits are implemented.
The arrangement of FIG. 2 thus provides bi-directional communication on each of the twisted pair data connection 60. Data communication over a single pair, thus obviating the need for a structured cable of 4 twisted pairs, is similarly possible using arrangement 100, has been commercially implemented, and is commonly known as single pair Ethernet.
Disadvantageously, the arrangement of FIG. 2, when utilized for single pair Ethernet does not provide a plurality of powering paths over twisted pair data connection 60 which would result in no net flux. This is particularly true, since with a single twisted pair, the power and return paths must be provided over only the 2 wires of twisted pair data connection 60.
U.S. Pat. No. 8,044,747 issued Oct. 25, 2011 to Yu et al., entitled “Capacitor Coupled Ethernet”, the entire contents of which is incorporated herein by reference, provides a system and method for enabling power applications over a single conductor pair. In one embodiment, data transformers are coupled to a single conductor pair using one or more direct current (DC) blocking elements that preserve an alternating current path. Power is injected onto the single conductor pair after the DC blocking elements and power is extracted from the single conductor pair before the DC blocking elements. Disadvantageously, such a solution places the one or more DC blocking elements in the data path before the detecting element, which may lead to signal degradation.